TRPV4 (transient receptor potential vanilloid 4) channel-dependent negative feedback mechanism regulates Gq protein-coupled receptor-induced vasoconstriction

Abstract

Objective-Several physiological stimuli activate smooth muscle cell (SMC) Gq PCRs (Gq protein-coupled receptors) to cause vasoconstriction. As a protective mechanism against excessive vasoconstriction, SMC Gq PCR stimulation invokes endothelial cell vasodilatory signaling. Whether Ca2+ influx in endothelial cells contributes to the regulation of Gq PCR-induced vasoconstriction remains unknown. Ca2+ influx through TRPV4 (transient receptor potential vanilloid 4) channels is a key regulator of endothelium-dependent vasodilation. We hypothesized that SMC Gq PCR stimulation engages endothelial TRPV4 channels to limit vasoconstriction. Approach and Results-Using high-speed confocal microscopy to record unitary Ca2+ influx events through TRPV4 channels (TRPV4 sparklets), we report that activation of SMC a1ARs (alpha1-adrenergic receptors) with phenylephrine or thromboxane A 2 receptors with U46619 stimulated TRPV4 sparklets in the native endothelium from mesenteric arteries. Activation of endothelial TRPV4 channels did not require an increase in Ca2+ as indicated by the lack of effect of L-type Ca2+ channel activator or chelator of intracellular Ca2+ EGTA-AM. However, gap junction communication between SMCs and endothelial cells was required for phenylephrine activation or U46619 activation of endothelial TRPV4 channels. Lowering inositol 1,4,5-trisphosphate levels with phospholipase C inhibitor or lithium chloride suppressed phenylephrine activation of endothelial TRPV4 sparklets. Moreover, uncaging inositol 1,4,5-trisphosphate profoundly increased TRPV4 sparklet activity. In pressurized arteries, phenylephrine-induced vasoconstriction was followed by a slow, TRPV4-dependent vasodilation, re?ecting activation of negative regulatory mechanism. Consistent with these data, phenylephrine induced a signifcantly higher increase in blood pressure in TRPV4-/-mice. Conclusions-These results demonstrate that SMC Gq PCR stimulation triggers inositol 1,4,5-trisphosphate-dependent activation of endothelial TRPV4 channels to limit vasoconstriction.